Wastewater TreatmentBataan 2020, Inc.March 9, 2013

What is wastewater treatmentUsually refer to sewage treatment or industrial wastewater treatmentprocess of removing contaminants from wastewater

GoalsTo produce waste stream (effluent)To produce solid waste (sludge)To discharge or reuse them back into the environment

Where does wastewater come from?Residences (kitchen, bathroom)Commercial institutionIndustrial institution (usually require specialized treatment process)

How can it be treated?Collected and transported via a network of pipes and pump stations to a municipal/industrial wastewater treatment plant

3 stages of water treatmentPrimarysolids are separated Secondarydissolved biological matter is converted into a solid mass by using water-borne bacteriaTertiarybiological solids are neutralized then disposedtreated water may be disinfected chemically or physically

Types of treatmentMechanical treatmentInfluentRemoval of large objects Removal of sand and grit Primary Sedimentation Biological treatmentTrickling bed filterActivated sludgeChemical treatmentDisinfection

Preliminary treatmentRemove large objectsEx: sticks, rags, toilet paper, tamponsRaked screenClog equipment in sewage treatment plant

Treatment stages - Primary treatmenttypical materials that are removed during primary treatment includefats, oils, and greases (aka FOG)sand, gravels and rocks (aka grit)larger settleable solids including human waste, and floating materials

Methods used in primary treatmentSand catcherRemove sand and gritControl wastewater velocitySand grit and stone settleKeep suspended organic matter in waterDamage equipments in the remaining treatment stageLandfill

Primary Sedimentation TankRemove grease, oilFecal solid settle, floating material rise to the surfaceProduce a homologous liquid for later biological treatmentFecal sludge are pumped to sludge treatment plant

Treatment stages - Secondary treatmentDegrade biological content (dissolved organic matter) of the sewageEx: human waste, food waste, soaps, detergentAdded bacteria and protozoa into sewage3 different approachesFixed film systemSuspended film systemLagoon system

Three approachesFixed Film Systemsgrow microorganisms on substrates such as rocks, sand or plastic wastewater is spread over the substrateEx: Trickling filters, rotating biological contactors

Trickling filters bedSpread wastewater over microorganismmade of coke (carbonised coal), limestone chips or specially fabricated plastic mediaOptimize their thickness by insect or worm grazing

Suspended Film Systemsstir and suspend microorganisms in wastewater settled out as a sludge pumped back into the incoming wastewater Ex: Activated sludge, extended aeration

Activated sludgemixed community of microorganismsBoth aerobic and anaerobic bacteria may existBiological floc is formed

5 physical components of activated sludge processaeration tank oxygen is introduced into the system

aeration source ensure that adequate oxygen is fed into the tank provided pure oxygen or compressed air

secondary clarifiers activated-sludge solids separate from the surrounding wastewater

Activated sludge outflow linePump activated sludge back to the aeration tank Effluent outflow linedischarged effluent into bay or tertiary treatment plant

Lagoon Systemshold the waste-water for several months natural degradation of sewage Usually reeds are preferred

Treatment stages Tertiary treatmentremove disease-causing organisms from wastewater 3 different disinfection processChlorinationUV light radiationOzonation

Chlorination Most commonAdvantages: low cost & effectiveDisadvantages: chlorine residue could be harmful to environment

UV light radiationDamage the genetic structure of bacteria, viruses and other pathogens.Advantages: no chemicals are usedwater taste more naturalDisadvantages: high maintenance of the UV-lamp

OzonationOxidized most pathogenic microorganismsAdvantages: safer than chlorination fewer disinfection by-productDisadvantage: high cost

What can effluent use for?discharged into a stream, river, bay, lagoon or wetland used for the irrigation of a golf course, green way or parkIf its sufficiently clean, it can be used for groundwater recharge

Advanced TreatmentNitrogen removalAmmonia (NH3) nitrite (NO2-) nitrate (NO3-)Phosphorous removalPrecipitation with iron or aluminums saltLead to eutrophicationMay cause algae bloom

Sludge treatmentPrimary sludge usually have strong odorsSecondary sludge have high concentration of microorganismGoals of treatments are:Reduce odorsRemove water reduce volumeDecompose organic matter

Untreated sludge are about 97 percent water Settling can reduce about 92 to 96 percent of water dried sludge is called a sludge cake

3 different sludge treatmentsAerobic digestionAnaerobic digestioncomposting

Aerobic digestionBacterial processNeed oxygenConsume organic matterConvert into carbon dioxide (CO2)

Anaerobic digestionBacterial processDo not require oxygenConsume organic matterProduce biogas, which can be used in generators for electricity

Composting aerobic processrequires the correct mix of carbon, nitrogen, oxygen and water with sludgeGenerate large amount of heat

Sludge disposalSuperheat sludge and convert into small granules that are rich in nitrogenSell it to local farmer as fertilizerSpread sludge cake on the fieldSave landfill space

Summary

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